The present disclosure relates to an image forming apparatus and a control method for a fixing heater. More particularly, the present disclosure relates to an image forming apparatus and a control method for a fixing heater, with which the consumption current of the fixing heater can be increased within a range not exceeding a setting current of a commercial power supply.
When, as in a multifunctional peripheral, an entire system including an image forming apparatus to which are connected peripheral devices, such as an image reading device (reader), a post-processing device (feeder), and a large-capacity paper feed device (option cassette), is used with a general commercial power supply, the current consumed by the entire system needs to be set so as not to exceed a predetermined value (e.g., 15 A in Japan). Therefore, the image forming apparatus and the peripheral devices are designed to hold their maximum consumption currents such that the total of the respective consumption currents of the image forming apparatus and the peripheral devices is not greater than a predetermined value.
When the image forming apparatus is a laser beam printer, for example, the electric power consumed by the thermal fixing device of the laser beam printer is maximum, and rated power of, e.g., a halogen heater serving as a heating unit of the thermal fixing device is held relatively low in some cases. The relatively low rated power of the heater creates problems in that a longer time is needed for warm-up, and image having a fixing failure may be outputted regardless of whether the peripheral devices are connected or not.
To solve the problems mentioned above, there is proposed an image forming apparatus including a consumption current detecting member for detecting the consumption current of one or more peripheral devices, a thermal fixing device for thermally fixing a toner image to a recording medium, and a temperature detecting member for detecting a temperature of the thermal fixing device. The proposed image forming apparatus also includes a power calculator for calculating, based on information regarding the consumption current of the peripheral devices and obtained by the consumption current detecting member, an allowable maximum power applied to a heater located in the thermal fixing device such that the total consumption current of the image forming apparatus and the peripheral devices is not greater than a predetermined value. The proposed image forming apparatus also includes an energization controller for controlling, based on the temperature detected by the temperature detecting member, energization of the heater within a range up to the allowable maximum applied power calculated by the power calculator such that the temperature of the thermal fixing device is kept at a predetermined temperature. With such a configuration, the current consumed by an entire system including the image forming apparatus and the peripheral devices, such as a reader, connected to the image forming apparatus can be held so as to be not greater than the predetermined value without prolonging the warm-up time by lowering the rated power of the heater. This results in advantageous effects that the relevant system can be operated with the general commercial power supply, and that images having a fixing failure can be avoided from being generated.
Furthermore, a fixing unit is located in the image forming apparatus, the fixing unit includes a heat roller, an induction heating coil for heating the heat roller, a current detector for detecting an input current. To supplied to the entirety of the image forming apparatus, and a fixing unit controller for controlling power supplied to the induction heating coil. When the input current Io detected by the current detector exceeds a setting current value Is, the fixing unit controller in the proposed fixing unit outputs, to a control unit of the image forming apparatus, a power (Ws−((Io−Is)×Vin) obtained by subtracting a power ((Io−Is)×Vin), which is the product of multiplying a voltage Yin supplied to the image forming apparatus by an excess current value (Io−Is), from a setting power Ws preset for supply to the fixing unit. By being given that the power (Ws−((Io−Is)×Vin) output from the fixing unit controller, the control unit of the image forming apparatus outputs a power control signal representing a value of the given power to the fixing unit controller, causing the fixing unit controller to control power supplied to the induction heating coil, to thereby perform control such that the input current Io does not exceed the setting current value Is. Thus, the current consumed by the entire apparatus can be controlled such that it does not exceed a prescribed current value, by detecting the input current to the image forming apparatus and by controlling the power supplied to the fixing unit, which consumes a large current.
Moreover, there is proposed a control device for an image forming apparatus, the control device includes a current detecting member for detecting a first total current value in a particular system of power supply equipment, the particular system including the image forming apparatus, a predictor for predicting a current value used by the image forming apparatus, and a calculator for calculating a second total current value based on the first total current value and the predicted current value. The proposed control device also includes a comparison member for comparing a current capacity of the particular system of the power supply equipment and the second total current value, and operation controller for causing the image forming apparatus to execute particular processing depending on a comparison result of the comparison member such that a circuit breaker is not turned off. Thus, the proposed control device allows only the particular processing to be executed by previously predicting the occurrence of a problem due to an overcurrent at such a level as turning off the circuit breaker, and by effectively distributing the limited power so as to avoid the occurrence of the problem. Hence it is possible to prevent troubles caused by frequent turning-off of the circuit breaker while ensuring safety.
As discussed above, the energization control for the fixing device in the image forming apparatus is executed as a control for keeping the temperature of the fixing heater constant. However, when a fixing process is performed on a certain sheet, the sheet draws heat. Accordingly, under setting conditions to execute the image forming process on a large number of sheets per unit time, particularly, the energization control is preferably performed on the fixing heater as far as up to an allowable maximum limit during the execution of the image formation.
In addition, the energization control is usually required to be performed within a range that such the total consumption current consumed by the entire image forming apparatus does not exceed the setting current (rated current 15 A) of the commercial power supply. To that end, in the above-described image forming apparatus, the total consumption current is detected or predicted, and when the total consumption current exceeds a predetermined setting current, the consumption current of the fixing heater is controlled to be reduced for a certain time.
Meanwhile, as mentioned above, various peripheral devices consuming currents are connected to the image forming apparatus in many cases. When a punching or stapling operation is executed in a post-processing device among the peripheral devices, the consumption current of the relevant peripheral device temporarily increases to a great extent and the total consumption current of the image forming apparatus temporarily increases. Depending on not only the types of circuits incorporated in the image forming apparatus and the peripheral devices, but also the type of power distribution environment of the commercial power supply, the total consumption current of the image forming apparatus may also temporarily increase during execution of the image formation due to other causes than the punching or stapling operation.
In such a case, as described above, the consumption current of the fixing heater is controlled to be reduced for a certain time. However, the reduction in the consumption current of the fixing heater directly leads to a temperature drop of the fixing heater. This may cause a problem of degradation in fixing property (i.e., quality of a formed image). If a process of reducing a sheet conveying speed is executed, for example, to deal with the problem of degradation in fixing property, the process naturally raises another problem of reducing a throughput of the entire image forming apparatus.
On the other hand, except for the period during which the total consumption current of the image forming apparatus temporarily increases, the consumption current of the fixing heater needs to be maintained at as great a level as possible, because the total consumption current is comparatively low.